[jira] [Commented] (KAFKA-3745) Consider adding join key to ValueJoiner interface

["Bill Bejeck (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KAFKA-3745?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17286622#comment-17286622 ] 

Bill Bejeck commented on KAFKA-3745:
------------------------------------

Taking the overloaded method approach with the Scala API causes an issue with an "Ambiguous reference to overloaded definition" issue.  I'll investigate and provide a follow-on PR.  The current PR changes to the Java API [https://github.com/apache/kafka/pull/10150] do not cause any issue with the Scala API.  I think considering this is a new addition it's acceptable to take an approach where we add this new functionality in steps

> Consider adding join key to ValueJoiner interface
> -------------------------------------------------
>
>                 Key: KAFKA-3745
>                 URL: https://issues.apache.org/jira/browse/KAFKA-3745
>             Project: Kafka
>          Issue Type: Improvement
>          Components: streams
>    Affects Versions: 0.10.0.0
>            Reporter: Greg Fodor
>            Assignee: Bill Bejeck
>            Priority: Minor
>              Labels: api, kip
>
> In working with Kafka Stream joining, it's sometimes the case that a join key is not actually present in the values of the joins themselves (if, for example, a previous transform generated an ephemeral join key.) In such cases, the actual key of the join is not available in the ValueJoiner implementation to be used to construct the final joined value. This can be worked around by explicitly threading the join key into the value if needed, but it seems like extending the interface to pass the join key along as well would be helpful.
> KIP-149: [https://cwiki.apache.org/confluence/display/KAFKA/KIP-149%3A+Enabling+key+access+in+ValueTransformer%2C+ValueMapper%2C+and+ValueJoiner]



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